This invention relates to an electronic copying apparatus, and more particularly an electronic copying apparatus having a photosensitive drum which has a drum body with a photosensitive layer laid on its pariphery.
The photosensitive drum of a known electronic copying apparatus comprises a drum body with a hollow cylinder and a photosensitive layer laid on the outer periphery of the drum body. The cylinder is made of a metal, usually aluminum, because it must be electrically conductive and strong enough to maintain its circularity. The photosensitive layer is made of selenium (Se) or cadmium sulfide (CdS), either vapor-deposited or coated over the outer periphery of the drum body, and has a uniform thickness.
Made of a metal, the cylinder is heavy. The mechanism supporting the photosensitive drum is inevitably large, and so is the mechanism for driving the drum. This raises the manufacture cost of the copying apparatus. Further, the photosensitive layer wears, and the lifetime of the drum is limited. The drum needs to be replaced by a new one when its photosensitive layer is found no longer effectively functioning. A repairman replaces an old drum with a new one. His work is rather hard and cumbersome since the drum is heavy. The old drum is thrown away. If its cylinder is made of an expensive metal, its running cost will rise.